Nomogram-based estimate of axillary nodal involvement in ACOSOG Z0011 (Alliance): validation and association with radiation protocol variations.

PURPOSE: A substantial proportion of patients enrolled on ACOSOG Z0011 received protocol-deviant radiation treatment. It is currently unknown whether these deviations involved the use of more extensive fields in patients at higher nomogram-predicted risk.

METHODS

We used the M.D. Anderson (MDA) and Memorial Sloan-Kettering (MSK) nomograms to estimate risk of additional positive axillary nodes using surgical pathology information. In the control arm, we compared axillary dissection (AD) findings to nomogram-predicted estimates for validation. We used logistic regression to evaluate whether nomogram-estimated higher risk of nodal involvement was associated with high tangent (HT) or supraclavicular (SCV) radiation fields for patients with known radiation field design.

RESULTS

552/856 (64.5%) had complete details for the MDA nomogram. Mean MDA risk estimate in both treatment arms was 23.8%. Estimated risk for patients on the AD arm with positive nodes was 25.9%. Higher risk estimate was associated with additional positive nodes in the AD arm (OR 1.04, 95% CI 1.02-1.06, p < 0.0001). We observed significant association with higher MDA nomogram-estimated risk and SCV radiation (OR 1.07, 95% CI 1.04-1.10, p < 0.0001) but not HT (OR 0.99, 95% CI 0.96-1.02, p = 0.52) The MSK nomogram had similar associations.

CONCLUSION

MDA and MSK nomogram risk estimates were associated with lymph node risk in ACOSOG Z0011. Radiation oncologists' use of differing radiation fields were associated with treating higher risk patients. ClinicalTrials.gov id: NCT00003854.